Throw the user-friendly message when error caused in optimizer of graphd

[yixinglu]

Introduction

Before #4956 , the error caused in optimizer will be passed to user directly, some errors are not easy to understand since there are many strange terms and concepts in optimizer for nebula user.

After that the errors have be unified into the following one:

There are some errors found in optimizer, please contact to the admin to learn more details

this also will be hard to be understood and the user don't know what to do next. Maybe the message could suggest the user to check the nebula-graphd.INFO log to learn more error details.

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